The present invention relates on a brazing method for an aluminum or aluminum alloy work.
As methods for spreading a brazing to an aluminum or aluminum alloy work, a method utilizing electrostatic induction and a method by which a brazing flux dissolved in water is sprayed are known. In the case of the method utilizing electrostatic induction, the work is electrically grounded and a powdered brazing flux is charged by electrostatic induction. The charged brazing flux is carried to the work by a coulomb force, and thereby the brazing flux is spread to the work. In the case of the method by which a brazing flux dissolved in water is sprayed, a flux-mixed liquid is prepared by mixing a powdered brazing flux with water, and the flux-mixed liquid is sprayed to the work. After spraying, drying (for example, at 140.degree. C. for 5 minutes) is performed, and thereby the brazing flux is fixed to the work.
FIG. 6 is a perspective view showing an example of a flat tube used for a heat exchanger of an air-conditioning system. A flat tube 1 is composed of a one-piece sheet made of an aluminum alloy. In the flat tube 1, there are formed three coolant paths 5, 6 and 7 by brazing inside faces of embossed portions 2, 3 and an inside face of an end portion 4. Flat tubes 1 like this are produced by continuously forming a rolled aluminum alloy sheet by an endless processing and cutting it into individual flat tubes in the final stage of forming.
In the case of a flat tube like this, it is not possible to spread the brazing flux to inside faces of the embossed portions 2, 3 and inside face of the end portion 4 after the flat tube 1 is formed as shown in FIG. 6. For this reason, it is necessary to spread the brazing flux in the middle of forming the flat tube 1. However, the method utilizing electrostatic induction cannot be used for spreading the brazing flux in the middle of forming. That is, since the work is electrically grounded and the brazing flux is charged for spreading in the method utilizing electrostatic induction, it is necessary to conduct the spreading of the brazing flux separately, or as an independent process, after cutting flat tubes 1 into individual pieces. Accordingly, it is physically not possible to incorporate the spread of the brazing flux into the endless process. In addition, since the brazing flux is spread in a dry state, the fixing character of the brazing flux is not so good. On the other hand, in the case of the method by which a brazing flux dissolved in water is sprayed, the work must be dried and in order to fix the brazing flux on the work after the spread of the flux-mixed liquid. Hence, when the spread of the brazing flux is incorporated into the endless process, a drying time is required, and the result is an adverse effect to the speed of forming the flat tubes 1.